May 2010

Mining at depth

Seafloor massive sulphide deposits closer to development

CIM Distinguished Lecturer Steven Scott’s presentation on seafloor massive sulphide (SMS) mining has grown over the years. He has added new information on exploration tenements, updated the activities of the handful of mining companies exploring the oceans for deposits rich in copper, gold, silver and zinc, and noted the creation of new ventures — most of which the retired University of Toronto faculty member has consulted for. He has created versions of his presentation that cater to the expertise of his audience and translated his vast knowledge of undersea hydrothermal geology into French. The most significant development, however, may be what has been removed. Until recently, the subtitle of Scott’s talk, “The dawning of a new industry,” ended with a question mark.

Seafloor mining is no longer beyond the horizon. Last December, Australia-based and TSX-listed Nautilus Minerals was granted an environmental permit from the government of Papua New Guinea, and the company expects a mining licence to follow this year for its Solwara 1 tenement off the eastern shore of the mainland. There are no shafts to sink, no housing to construct or overburden to remove. A seafloor mining tool can be lowered down to cut and vacuum up the rich deposits. “Depending on financing, we expect to start production in mid-2012,” says Scott Trebilcock, vice-president, business development and investor relations at Toronto-based Nautilus. The property is 1,600 metres below the surface of the Bismarck Sea, a tiny but potentially lucrative piece of the more than half million square kilometres in the South Pacific that the company has either secured or applied for prospecting rights to.

Gilded black smokers

Ore deposits on land give only subtle hints of their presence. Under water, active hydrothermal vents in many of the seafloor sulphide zones announce themselves with plumes of “smoke” made black by the precipitation of dissolved metal sulphides and other minerals. Chimneys rich in minerals belch water that has seeped through fissures in the seafloor and been superheated and enriched by the magma below. These black smokers exist across the world’s oceans, churning out natural resources with industrial efficiency. According to the 2007 NI 43-101 estimate of the mineral resources at Nautilus’ Solwara 1, the indicated resource is 870,000 tonnes with a copper grade of 6.8 per cent, with 23 grams of silver per tonne and 4.8 of gold. The inferred resource is 1,300,000 tonnes with a copper grade of 7.5 per cent, 37 grams of silver per tonne and 7.2 of gold. That high grade dictates the scale of underwater projects, says Scott. “On land, we geologists are looking for elephants. In the sea, we can do well just finding the elephant turds, so long as there are enough of them.”

Breaking ground underwater

To chart the future of deep-sea mining, Scott looks back to the development of the offshore oil and gas industry. Since the 1940s, when the first offshore platforms began producing, the oil drawn from beneath the oceans has become a large portion of the overall supply, about 30 per cent and growing. It is also one of the well-established industries from which deep-sea miners will draw technical expertise, says Trebilcock. “All the different components — the hydraulics, the pressure seals, the control systems, the tracks — are proven technologies. The key piece of equipment, the seafloor mining tool, even though it is custom-designed for our application, is based on deep-sea trenching machines.”

The ore, Trebilcock explains, will be cut from the seabed by the mining tool and then pumped as a slurry up a 1.6-kilometre pipe to the surface. On ship, the ore will be dewatered and transferred to a barge. “Once we get it onto the ship, it’s like any other volcanogenic massive sulphide process,” he says. “It’s the same metallurgical processes. We float it and get a copper concentrate with gold credits.”